1. Field of the Invention
The invention relates in general to a broadband antenna, and more particularly to a broadband dipole antenna that is fed at one short side to enlarge the antenna bandwidth.
2. Description of the Related Art
Along with technological progress, the need for broadband antennas has been increasing rapidly. For example, people can easily watch digital TV via portable TV products. Digital TV is a television system which converts analog signals to digital signals, and Taiwan now uses a European digital video broadcasting terrestrial (DVB-T) system. The DVB-T system can effectively solve a multi-path interruption problem by using modulation standard signals. The European-specification system constructs a single frequency network (SFN) to increase accessible frequency spectrum resources. In addition, the European TV system has a feature of mobile reception and thus people can watch TV even in a car running at a high speed of 130 km/hr.
For example, in early periods, antenna technologies of advanced channel estimation and dual antenna reception for distribution and integration were developed in order to improve mobile reception function of the DVB-T receiver disposed in a car. However, these technologies resulted in system complexity, higher hardware costs, and higher antenna power consumption. In the present market, a conventional digital TV antenna used in a car is a monopole antenna. The monopole antenna uses the car shell as a grounded surface, but this greatly affects the appearance of the car and and decreases the car's attractiveness. Also, due to the shielding effects of the car's metal shell, the antenna's ability to receive signals becomes degraded.
Recently, technology of a dipole antenna for digital TV reception has been developed. Conventionally, owing that signals are fed into the central part of the dipole antenna symmetrically via a coaxial line, the coaxial line will not be parallel to the direction of two arms of the dipole antenna. Therefore, in practical application, the coaxial line needs to be perpendicular to the digital TV antenna, thereby increasing the volume of the antenna. When the digital TV antenna is disposed in a car, it will further affect the aethestic appearance of the car. In addition, due to the narrow width of the antenna's radiation conductor, the antenna's bandwidth may be inadequate.